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Me Talk Pretty – Pyrexia

That’s right, it’s time for another super sexy physiology term. Pyrexia (known on the streets as a fever) is one of the most well known signs that “something ain’t right.” Here’s an obnoxiously obvious statement to start your day; the human body is all about balance. For example, our body is only really happy if it’s core temperature is maintained within roughly 36.5-37.5 C or 97.7-99.5 F. That’s a pretty tight range for a lot of metabolic processes to take place. You’ll find more leg room flying coach. We have a temperature set point that our body is practically calibrated to. When we are experiencing hypothermia or hyperthermia the temperature of the environment we are in has affected our core temperature and pushed us beyond our cozy little set point. HOWEVER, a fever occurs when something triggers the body to temporarily raise it’s set point. That “something” is typically an infection (bacterial, viral, etc.). When this happens our immune system is making a declaration of war on the offending pathogen, turning up the heat.

Fevers happen when a pyrogen (thing that triggers a fever) causes the release of potent chemical messengers (produced by our cells) called prostaglandins that work on our hypothalamus. If you recall, our hypothalamus is our brain’s team captain of homeostasis with such popular hits as hunger, thirst, hormonal control, and temperature regulation. We love the guy but probably wouldn’t invite him to hang out very often because he would want to control EVERY little thing.
On the one hand, a fever creates a less cozy temperature range for the pathogen to thrive and reproduce. It has also been shown that the activity of immune cells like neutrophils (your marines on the ground) and T-cells (CIA operatives providing intelligence on the enemy) is greatly enhanced. This is basically the fight they’ve been training for their entire, short little lives. On the other hand, raising the body’s set point takes a lot of energy. When our temperature rises the small vessels at the surface of our skin constrict to conserve heat for the sake of our core. We start to shiver, which generates heat by our muscles while demanding more energy from our already weakened body. As we begin to adjust to our new set point we get warm and sweat to cool back down, losing water and salts. It’s no suprise that you feel so wiped out after you’ve recovered from a fever. So is a fever worth all that trouble or is it simply an evolutionary relic, a souvenir of our adaptive immunity’s epic saga of trial and error? It’s interesting that such a metabolically demanding process that can often spiral out of control (reaching temps of 105 F in cases of severe infection or autoimmune response) would stay with us. Despite it’s cost or contribution to our body’s war on bio-terror, we are not the only chosen ones on this planet to get the shakes and the sweats. Many other vertebrates and invertebrates from Rottweilers to Iguanas have been shown to exhibit fever-like responses to infection. Oh yeah, pyrexia gets around and it looks like she’s here to stay.